By Janet Krenn
A dull THUNK sound marks every step Jessica Thompson and her students take. For now, their plastic shoe attachments, called Mudders, provide background noise as they move buckets from their Jeep into an empty parking space in the Virginia Zoo lot. But when the Christopher Newport University research team leaves the blacktop and wades into the Lafayette River, the Mudders will keep them from sinking and getting trapped in the soft muck.
By risking the freedom of their feet, the Virginia Sea Grant-funded research team will attempt to discover whether living shorelines, man-made grassy banks that stop shoreline erosion, might also provide suitable habitat for an important feeder fish called a mummichog.
Mummichogs are finger-length fish that eat mosquito larvae and other small critters in and around muddy shores. More importantly for humans, however, blue crabs and striped bass eat mummichogs. If living shorelines could serve the dual purpose of stopping shoreline erosion while providing habitat for these little fish, the grassy banks could indirectly support some of Virginians’ favorite seafood species.
To determine whether living shorelines provide suitable habitat, Thompson and her students will look for evidence that mummichogs released near living shorelines are behaving and growing normally.
Earlier in May, the research team tagged more than 3,400 mummichogs from six different study sites along the coast of the Lafayette River in Norfolk and measured the length of each fish. They implanted little orange tags under the belly skin of the fish and then released them all at one release location per study site.
Releasing the fish together is key to determining whether they’re behaving normally. Mummichogs don’t typically move very far along a shoreline, says Thompson. “Normally they should just swim in and out with the tide.”
The team will return to their study sites throughout the summer and set traps at different places along the shoreline. If the fish are finding desirable habitat near living shorelines, most of the tagged mummichog should show up in the traps near the release site.
So far, that seems to be what is happening at one sampling site. When Virginia Sea Grant caught up with the research team on May 21 along the 400-foot living shoreline at the Virginia Zoo, 39 tagged mummichog were recaptured at the release site in the middle of the living shoreline, while only 8 were captured at either end.
“That’s a good sign that even in a living shoreline, they’re not moving much,” Thompson said.
But Thompson is finding that not all living shorelines are equally suitable. At the Hermitage Museum sampling site, there seems to be a lower abundance of mummichog, indicating those fish have roamed away from the area or died. Thompson wonders whether this could due to the stronger waves at Hermitage.These waves carry away fine sediments and leave behind a sandy environment that could create challenges for mummichogs as they look for food.
“Mummichog can utilize many food resources, but they definitely do rely at least in part on organisms that live in the mud and feed on detritus, so food may be limiting,” said Thompson; adding, “I am looking forward to analyzing the growth rates at the sites to see if the data support that hypothesis.”
Thompson is finding that there are many factors that could influence mummichog abundance. The width of the shoreline, for example, or even the placement of the shoreline within the watershed, could make a difference in fish abundance, growth, and survival.
“[T]his initial study has really convinced me that a larger study with a larger number of living shorelines will be needed to try to determine the effect of different living shoreline characteristics on resident fishes,” Thompson said.
By the end of this summer, however, Thompson and her students will have made the first steps in understanding how living shorelines can affect mummichog populations. Until then the team will continue strapping on those plastic Mudders and pulling in their data, one mummichog at a time.
Training Future Scientists
Thompson isn’t just gathering useful information for fisheries managers, her Virginia Sea Grant-funded study is also training five undergraduates from Christopher Newport University in the scientific process. Learn more by watching this slideshow.